Drop orphaned C8::S1 comments in rdoc_store_test.rb

tompng pointed out on #1690 that the
"C8::S1 does not exist. It should not be in the list."
comments in test_all_classes_and_modules and test_all_classes
were anchored to the Ripper-only workaround
("expected = (expected + ['C8::S1']).sort unless using_prism_ruby_parser?")
that the previous commit removed. With no workaround for them to explain,
the comments are orphaned -- drop them.

The matching comment in test_load_single_class stays; it explains the
remaining `assert_nil @c8_s1` assertion.

Author: claude

test/rdoc/rdoc_store_test.rb

@@ -166,9 +166,6 @@ def test_all_classes_and_modules
       Parent
     ]
 
-    # C8::S1 does not exist. It should not be in the list.
-    # class C8; class << something; class S1; end; end; end
-
     assert_equal expected,
                  @store.all_classes_and_modules.map { |m| m.full_name }.sort
   end
@@ -220,9 +217,6 @@ def test_classes
       Parent
     ]
 
-    # C8::S1 does not exist. It should not be in the list.
-    # class C8; class << something; class S1; end; end; end
-
     assert_equal expected, @store.all_classes.map { |m| m.full_name }.sort
   end